A device that allows multiple parties to communicate over the phone. Conference bridges can be manned by a proctor or operator, or they can be supervised. Some PBXs (Private Branch Exchange) include standalone conference bridges as well as conference bridge functions These systems include circuitry that sums and balances the energy (noise) on each channel so that everyone can hear each other. More sophisticated conference bridges can “idle” the transmit side of non-speaking parties’ channels.